The Unending Battle
by ManOfChocolate
Summary: In a bid to grow stronger, Asriel and Frisk sign up to learn the art of boxing under Undyne's supervision. Over the course of the training from hell, it soon becomes clear that there are other motives behind the children's sudden interest in fighting and not all of them innocent. For not all battles are fought within a ring.


**A/N: Fresh crosspost from Ao3! Unfortunately, I have no idea how actual boxing practice goes. Please, do not punch me if I get this wrong! I am but a frail piece of chocolate!**

* * *

"Undyne, is everything okay? Why are you crying?"

Undyne sniffed loudly and wiped her face, the signature toothy grin spread all across her, despite the tiny droplet running down her cheek. She promised herself she would never do this, especially not in front of the children, but there was just no way she could resist. After such a long time, here they were, locked in this beautiful moment. Frisk and Asriel together, clad in plain new gym clothes fresh off the rack, ready to be wrinkled, beaten, torn and drenched in sweat. Their gaze alternated between Undyne and the ring behind her, just freeing up after a presumably exhausting training session.

"Nothing." she sighed, trying to smear the tear even more with the pair of training gloves she was holding. "Just... savoring this moment."

Their innocent eagerness was exhilarating.

Frisk and Asriel glanced at each other and flashed a brief grin. They knew Undyne would be very happy to teach them, but they didn't think she'd get so emotional over it. It seemed like the long-standing leader of the Royal Guards had a special kind of soft spot for people willing to learn from her. Even without words, there was a common sentiment shared between the two. Perhaps, in her happiness, Undyne would go easy on them.

The thought lasted exactly until she brought her foot down, making both children flinch and revert their focus.

"Listen up, punks!" she exclaimed, the spark of determination glinting in her eye mixed with dangerous glee. "If you've come to me, that can only mean one thing: you're here to learn how to knock some heads together! Lucky for you I'm an expert at that, so get ready, because by the time we're finished here, you two will be packing some serious firepower in those fists. Now, get in the ring, on the double!"

Undyne's rousing holler echoed off the walls as the two scrambled over each other, making just about every other human and monster in the building smile. They knew exactly what was coming and while it was entirely likely the kids would return home hurting all over, they'd also come back for more the next day. Such was the magic behind Undyne's training regiment. The monster grinned and followed the two, opting to just vault into the ring rather than walk around.

The first couple moves were almost like a blur. It was obvious this wasn't the first time Undyne taught someone the basics of boxing, as she was perfectly aware of positioning and all the basic moves necessary to get started. The kids followed as best as they could, though their short and stocky builds didn't exactly manage to follow the monster's lithe and highly athletic frame.

"Here, try it like this." she said, adjusting Asriel's foot just a little more. "And watch your posture! You're so stiff I could topple you just by blowing in your direction!"

"Nu-uh, I'm like a big boulder, just like dad!" the little boss monster stated, though he did wobble a bit.

Frisk leaned forward from their previously frozen pose, just to watch what would happen. Undyne grinned and leaned down, wiggling her eyebrows.

"Is that so?" she asked. "You do know I suplex boulders, right?"

With that, she reached out, lightly poking the monster's side. Asriel gasped and trembled all over, but managed to hold his ground. This only spurred Undyne even more as she continued poking, right until she touched a ticklish spot. That sent Asriel into a giggling frenzy, breaking their stance. He almost fell into a sit, but managed to hold on at least that much, blushing as they heard Frisk chuckling along.

"That wasn't fair!" he complained, face red and flushed.

"Tell that to Asgore." Undyne stood up again and ruffled the goat monster's hair a bit. "I can't even count the times he beat me with cheap shots like this!"

Frisk stepped over and pat Asriel on the back as encouragement, only to make him even more embarrassed. Undyne briefly left the two, fetching some more equipment for the next round.

"Stop that." he whined, covering his face with large, fluffy ears.

"Hey! Playtime later, we're supposed to be fighting over here!" Undyne called out, returning with a large, striped boxing bag.

She set it down and grabbed the bag from behind, while the kids gathered their training gloves. The gloves were worn and faded with time, but by the looks of it, they have obviously served at least several sets of students over their lifetime of combat. Fastening the straps just like Undyne instructed, the two approached once again, now geared up and ready.

"Well then kiddies, it's time we pushed this further!" she said. While the gym was slowly emptying out, the people still there continued to observe the fish monster's boxing lessons with amusement. "I want each of you to hit this bag as hard as you can, okay? Think you can do that?"

They nodded in unison, determination burning in their hearts.

"Alright, that's what I like to hear!" she pumped her fist into the air, before returning to hold the bag. "You're up first, Frisk! Gimme all you got! No sparing this bag, just come out here and let 'em have it! Put all that human spirit to the test, power up and punch it right-"

She paused as Frisk casually walked over to the bag and wrapped their arms around it. They even went so far as to rub their face against the ragged surface, while locking it in their tender embrace. Undyne leaned over the bag with a look on her face somewhere between metal-smelting anger and boundless amusement.

"Are you really just here to make my life difficult?" she asked, tilting her head at them.

Then again, she would have been very surprised if Frisk showed any affinity for fighting at all. Just as when they had met, the child remained steadfast in their view of never hurting anyone. Undyne has tried many times to make them back out of that promise, but Frisk was determined to uphold those values till the end and even she knew how to identify an unwinnable battle.

Asriel on the other hand, proved a completely different bundle of difficulties. He tried, he tried oh-so-hard to strike on target, but every time the monster was about to land a hit, he closed his eyes and his aim fell flat. Still, at least the decision was firm behind the punch and Undyne couldn't really ask for too much more on a first attempt. Then again, going easy on them would also have been completely unlike her though.

As long as the kid had the guts to try, she was more than ready to accommodate him. Perhaps all he needed was a different approach.

"I think this his going to be familiar for you, Frisk." she chuckled, kneeling behind the child as they prepared for the next exercise. "You just have to do what you do best and don't get hit."

The knowing, perhaps even accusatory glance from the child only made her grin even more. Undyne double-checked the helmet and fastened the arm pads a little tighter as well, making absolutely sure to minimize the chance of any real injury. Asriel waited timidly before them, rubbing his gloved hands together. The thought of fighting Frisk wasn't exactly on top of his list of things he really wanted to try, but as long as it was just training, there was nothing to feel guilty about.

Once the fight began in earnest, he realized there really was no reason to be afraid, let alone guilty.

He couldn't land a single hit anyway.

Asriel stepped forward and pushed all his momentum into a punch, only to once again bash against nothing, but air. Frisk only had to step aside and while they were decked in more protective gear than they could count, it was like it didn't even matter. One blow after another, they spun, twirled, stepped and even jumped at one point, easily avoiding all of the goat monster's valiant attempts. By the time Frisk just began to break a sweat, Asriel was a heaping mess of exhaustion and perspiration, despite Undyne's insistence that this barely even qualified as training. He agreed, this was much more akin to an endless excursion into futility.

A series of loud noises made all three of them flinch though. It started with just one shrill chime, only to be followed by several more over the course of a few minutes. Asriel blushed, recognizing the noise as his phone. Frisk did as well and pulled the arm pad to their ear, signaling for Undyne that he probably got a whole series of messages by now. She grinned and leaned back against the ropes, waving her hand.

"It's alright, Asriel, grab yourself some water and check the phone before the damn thing bursts into flames." she said, only to roll her eye as both kids looked at her like she just said something irredeemably bad. The mistake dawned on her in a mere moment. "Oh come on, you've both heard me say a lot worse stuff before!"

Toriel's insistence to tone her language down in front of the two was annoying at best and infuriating close second. Considering the overzealous boss monster though, Undyne knew it was better if she just let Asriel answer the texts, most likely sent by her. He scurried right off, leaving her and Frisk alone for a couple minutes.

The human approached and leaned back against the ropes just like she had, sighing deeply. They were much better at hiding it, but it was pretty obvious they were also quite exhausted. Undyne made sure they would remember this little exercise and the best way of doing that was to ensure some sore muscles in the morning.

"You're a good kid." she said, smiling down at them. They looked up with a bit of confusion, not sure where to put the compliment, besides their heart. "It's really sweet of you to do this just for him. You don't care about boxing at all, do you?"

Frisk turned beet red and cast their gaze to the ground, mumbling something Undyne couldn't quite catch. She didn't need to though, that was the sweetest thing about them. They weren't nearly as hard to read as they thought.

"Don't feel bad, at least I'm giving you a good workout, too!" she chuckled, reaching down to ruffle their hair up a bit. Frisk reached up to brush her hand off, but she kept finding unguarded spots all over. Alas, their superb dodging did not extend to headpats. "Not everyone needs to be a fighter to be strong. You just be the wimpy loser with the big heart, okay?"

The familiar designation made them giggle.

"But mark my word, one of these days I'll get you to fight, you little scamp!" she added, noticing another figure enter the ring once more. "Back for more, Prince Dreemurr?"

"Huh?" Asriel raised his head for a moment, before nodding. His gaze was unfocused though, like he wasn't even really there. "Y-yeah, let's keep going."

Undyne and Frisk shared an odd glance, before they both assumed their previous positions.

"Ready?" she asked, raising a hand into the air. Frisk and Asriel both tensed up, preparing for the next round. "FIGHT!"

Asriel wasted no time in lunging forward, starting out with a left hook. As usual, Frisk moved to evade it, only to find the monster got just a little bit closer than expected. A full dodge was out of the question, but they still managed to avoid most of it with the arm pad. The punch connected, though the awkward angle made it merely graze the surface of the pad. Still, it was the first time all afternoon he got so much as close to a real punch, so it was a success in that sense.

Undyne remained silent, however.

Recovering quickly, he attacked again with a series of short jabs, aiming to throw the carefully dodging human's balance off. The tactic worked, and Frisk was soon forced to actively defend, rather than just step away from everything. Every punch and every blow made it harder and harder to keep up, soon the point of having to use the pads as shields, especially as Asriel was putting a lot more strength into his attacks, than before.

Their trainer watched the battle in silence, her eyes narrowing to every motion, every oddly aggressive reach. There was no playful banter, laughter or even a challenging little wink, either. He was fully invested in the fight; to win rather than just train. This normally would have pleased her, but the lack of a clear transition rubbed her the wrong way. There was little to no determination behind this change, but rather something else entirely. Something that didn't come naturally to the young prince.

Frisk let out a brief whine, the force of Asriel's punches quickly turning this training session into a surprisingly grueling endurance round. The monster may have been small and normally rather timid, but he did have strength to spare. He didn't even seem to be paying much attention, just stepping forward after every few hits, gradually backing Frisk towards the corner. The human held both arm pads up at this point, just hoping the wayward hits would land mostly on those, despite the waves of pain traveling up their arms by now. They uttered another whine, hoping against hope that they could rouse Asriel out of his mechanical onslaught, especially as another hook soared through the air, about to breach through their defenses completely.

The punch never connected though. Frisk opened their defenses, only to see Undyne's firm grasp locked around Asriel's wrist. It may just have been a mirage, but they could swear her eye was just about glowing, reminding the human that she wasn't the centerpiece of Asgore's defensive unit for nothing. Asriel flinched and immediately ceased attacking, but didn't say a single word. Rather, the fish monster knelt down before him and grabbed both gloves.

"I don't ever want to you see you do this again." she said. Despite the visible anger on her face, her voice was only mildly upset. "There are battles that might need all the fury you have, but this isn't it. You're not fighting a grand opponent, or to save anyone, you're just wailing against Frisk for no-good reason. This isn't what I'm teaching you. I'm teaching you to be better than this. To be a fighter, not a brute."

Asriel didn't raise his head, nor speak, but that trembling running through his body said more than enough. He jumped just a bit as Undyne touched his shoulder and glanced at her at least, only to see a kind, apologetic smile on her face, rather than the anger he expected. It was a surprisingly soothing sight. She did frown a little, as the familiar sound of her phone alarm went off, filling the gym with a particularly shrill, notably foreign singing voice.

"I'm sorry, but that's my cue. I gotta pick Alphys up." she said with a renewed smile, gesturing towards the loudly singing phone. "Shouldn't take more than half an hour, at most. I want you two to stay put and when I get back, we'll continue and we'll do it the right way, okay? Who knows, I might even show you a secret move or two, like that 'Dempsey Roll' Alphys found. Would you like that?"

The little boss monster nodded. Frisk joined up with them, panting heavily from exertion.

"Good." she said, scratching the tip of his head. "Old Nick, the janitor, may act like he's deaf as a rock, but let him know if you need anything. I'll be back before you know it."

Undyne checked Frisk for any injures, giving them a soulful pat to the back that threatened to topple the poor child and have them land face-first on the floor. Afterwards, she jumped out of the ring and grabbed her things, mercifully silencing the still-blasting alarm. Passing by the janitor's office, the aging gentleman gave her the usual silent salute, before passing over her keys from the safety locker.

"Those kids better be in one piece when I get back, you hear me?" she asked, receiving the usual grunt of acknowledgement.

Nodding in return, she headed out the door, smile once again descending into a worried frown. The sudden shift in Asriel's behavior worried her, to the point where she decided to bring it up to Alphys as well as soon as they would meet. The two shared a similar timid nature and a surprising amount of familiarity.

Perhaps, she knew something Undyne didn't.

* * *

The splash of cold water was the most wonderful treat Frisk has had all day.

Ignoring every parental advisory about gradually cooling off, they stuck their head under the faucet and let it blast with full force. They let out a loud and very satisfied groan, smiling to the cold water running all across their head, reinvigorating their mind and body. Undyne's training was by no means easy, and Asriel's fervent attacks also tired them out quite a bit. A slice of pie and a nap right after in Toriel's warm embrace looked like a wonderful idea in the child's mind.

Now cooled off, Frisk grabbed the towel and dried their head off with renewed vigor. Once suitably dry, they filled up a water bottle and headed back into the gym area, the cold feeling sinking into their stomach this time. Asriel was apparently still going at the boxing bag nearby, reigniting the worry for their brother. He hadn't said a word ever since Undyne left, resigned to just punching that one bag over and over again. He barely even acknowledged them since.

Frisk sighed and sat down on the bench with their bags. While drinking from the bottle, they fished their phone out as well, just to check if anyone called. Compared to Undyne and Asriel, they usually kept their phone silent, not wanting to bother anyone with their silly jingles. As the display woke up, a ball of nerve pooled together in Frisk's throat.

 ** _You have 36 New Messages!_ **

A sickly feeling eroded all the vitality the cold water gave them. Frisk drank again, pressing the phone with a trembling finger to open the first of many.

 _*Greetings, partner!_

It was everything they feared. Asriel's sudden change was quickly gaining some context.

 _*Azzy's being a bore and won't answer me, so I'll just talk to my other favorite sibling instead. (o| ‿ |o)_

 _*I hope you're having lots of fun!_

 _*Because I'm not._

Frisk exhaled, fear gripping their throat once again. They almost didn't want to scroll further, but knew they had to. They had to be prepared.

 _*It's boring all alone._

 _*Mom's gone too._

 _*When are you coming home?_

 _*There were some pie and chocolate, but they're gone now. (o | ‿ | o)_

 _*Frisk, are you ignoring me?_

The child barely even noticed their grip tightening around the water bottle; the crunch of plastic far too quiet to reach them over the haze of steadily growing panic.

 _*I hope you aren't._

 _*That would be very rude._

 _*And you know I don't like it when you're rude. (o | ‿ | o)_

 _*Answer me._

Frisk was drinking nothing, but droplets from the bottle now. They were sweating once again, wincing from the salty perspiration biting into their skin on so many hidden contact points; mementos of the 'fun times' spent with their sibling.

 _*alright I'll make my own company_

 _*Azzy's stuffed toys seem like they could use a partner to play with_

 _*Look how much fun we're having!_

The message was accompanied by a photo this time around. Chara, surrounded by Asriel's collection of toys, like a monarch observing their subjects.

 _*oops (o | ‿ | o)_

Frisk stifled a whimper, as the message was accompanied by another photo. It was the head of a stuffed monster, crudely ripped off and placed on Asriel's pillow. Chara held the camera, smiling brightly while showing a peace sign with the other hand.

 _*okay this is getting boring_

 _*you're annoying_

 _*ANSWER ME_

 _*okay fine_

 _*you have to come home eventually_

 _*go and have your fun_

 _*ill wait_

 _*after all we're together forever aren't we_

 _*partner (o | ‿ | o)_

Frisk shut the phone off, refusing to look at any more messages. At this point, they had a fairly good idea of what to expect and none of it was good. It did, however, explain Asriel's behavior.

The prince was still bashing at the boxing bag with reckless abandon. Head hung low, not paying any attention to the outside world, as he wailed on the bag without mercy. The more he punched, the less he had to think about anything. And the less he could thing, the further their laughter and the glinting, blood-red eyes traveled from him. Far away, from where they could never reach him again. Every hit hurt his hands by now, but it was a good hurting, something that kept their mind off what awaited them back home; the never ending trials that did not cease for a single second.

The home he loved and lost.

The home he wished to return to, for so long.

The home Frisk made into reality.

And the home that twisted into a nightmare afterwards.

"Asriel?"

It was the voice again, the sweet voice, the one dripping with barely-contained malice. Without thought or purpose, he hooked the next punch from behind closed eyes and it landed true. A sickening thump, a loud whine of pain and an equally loud thud were the sequence of noises that finally brought him back to the present at hand. Asriel picked his head up again, the red cloud dispersing from his vision, only to see Frisk lying on the floor, curled up and gripping their face.

Asriel's soul felt like it had cracked and exploded into a million pieces.

"Frisk!" he cried, throwing the gloves aside and kneeling down next to his sibling. He carefully held the frail human, mindful of the parts only he knew hurt all the time. The painful realization burned in his mind. He hurt the one person he solemnly vowed never to cause pain to again.

"I'm sorry, Frisk I'm so sorry, I-I-I didn't meant to do it!"

It was a lie and he knew it. The only thing off was the target, not the intention.

The child whimpered loudly, tears streaming down their quickly swelling face. Asriel couldn't hold his own tears in, guilt clawing at his heart stronger than any monster could.

"I'm sorry..." he sobbed. "I'm sorry, I'm sorry, please..."

It hurt. It really did hurt with a pulsing ache, but without the sharpness broken bones or teeth would have suggested. Frisk sniffled and reached up, stroking the white fur on Asriel's cheeks. They couldn't yet produce the smile they wanted, but it was the most comfort they could offer.

"I'm sorry..." he continued, hiccuping through the tears. Frisk knew this wasn't about the punch anymore. There was a deeper, ever-present wave a guilt that lingered beyond that. "I can't do this... I thought... I thought t-they changed. I thought I was... sure of it. That m-maybe we could be a family... a real one..."

It was a regret that never should have occurred in the first place and a remorse that should not have been his to bear.

"I convinced you... begged you... and now this... this is what..." he could barely continue through the waves of sobs.

Frisk reached up and pulled him close, refusing to let the monster finish his self-destructive lashing. The goat monster was still shaking all over, but stopped talking and just held onto his sibling. They sucked the air in a bit, the force of his hug touching upon some of the bruises layered on their back, but they also knew Asriel had plenty of them as well. They were just easier to hide under all that fur.

They both had plenty of marks upon them.

Two two remained like that for what seemed like hours, rocking back and forth in an embrace of sorrow and unhealed wounds, sobs and sniffles gradually quieting down. Even the silence was comfort enough, so long as they got to be in it together.

"What're we going to do?" Asriel breathed, tear-filled fur bristling against Frisk's unhurt cheek.

Frisk reached out and grabbed Asriel's hand. The monster was still very far from the kind of growth spurt that would lead him towards a stature like his father's, but his hands were already big enough that their needed their own two to cover it up. They gripped the hand with all the force they could muster, though no voice would or even could leave their throat right now. Asriel paused for only a second, before pulling them closer again. The red glow of Determination burned against the boss monster's essence, souls pulsing in a kind unison.

He knew the answer, deceptively simple as it may have been.

They would survive.

They would fight back.

They would persevere.

And they would do it together.

* * *

 **Well, it's been a while, hasn't it?**

 **Unfortunately, I've been having a lot of work to deal with and it has eaten up quite a lot of my writing time. Hopefully, this should improve soon, but until then I thought I'd at least provide some reading material! This fic has actually been finished for a couple weeks now, but desperately needed a couple rounds of editing, which I just couldn't get to. It was once again a request, this time combining two different prompts, namely: "Frisk and Asriel learn boxing from Undyne" and "Frisk and Asriel learn boxing to escape Chara's bullying". Alas, kids can be quite cruel.** **Thought this may be too early to say, but with a little luck, this is the first time in a while I could say...**

 _ **THE CHOCOLATE FLOWS ONCE MORE**_

 **Comments, remarks, critiques and lists of favorite chocolates are all welcome by my Tumblr, Milkasingularity! Take care, dear readers!**


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